It is well known that the wear condition and/or breakage of a cutting tool can be determined by monitoring the force applied by the tool to a workpiece and that cutting force changes dramatically near or at the point when the cutting tool fails. By monitoring tool force, the failure or breakage of a tool can be predicted immediately prior to tool failure so that catastrophic damage to the workpiece by an unduly worn or broken tool can be avoided.
Others in the past have employed strain gage sensors for the purpose of measuring cutting forces, and thus cutting tool wear. Examples of strain gage and similar sensors are disclosed in the following U.S. patents:
______________________________________ U.S. Pat. No. Issue Date Title ______________________________________ 2,054,787 September 22, 1936 Measuring Device 3,596,506 August 3, 1971 Tool Force Monitor 3,872,285 March 18, 1975 Control System For Sensing the Vibration and Lateral Force on a Cutting Tool 4,487,078 December 11, 1984 Clamping-Force Transducer For Rotating Clamping Devices ______________________________________
These prior strain gage sensors have several disadvantages, however. Strain gage sensors which are desirably stiff lack the needed sensitivity for accurate force measurement. On the other hand, strain gage sensors having relatively high sensitivity lack the inherent stiffness needed to avoid compromising the overall stiffness (and thus, accuracy) of the machining apparatus. Additionally, in those machine tool systems employing multiple cutting tools mounted on a turret, it is necessary to mount a strain gage sensor on each cutting station of the turret, thus necessitating a relatively large number of sensors.